Piston pump for a vehicle brake system

ABSTRACT

To enable economical production of a piston for a piston pump, the piston is made from a tubular deformed part and a closure plug, which is press-fitted with a protrusion into the deformed part. The piston has the advantage that the piston can be made without metal cutting in the form of deformed parts, for instance by extrusion, and hence can be produced quickly and economically.

PRIOR ART

The invention relates to a piston pump which is intended for use as areturn feed pump for a slip-controlled vehicle brake system.

Such piston pumps are known per se. For example, see the piston pumpdisclosed in German Patent Disclosure DE 40 27 794 A1. This known pistonpump has a pump housing, in which a piston that can be driven to executea reciprocating stroke motion is axially displaceably received. Forfluid admission, the piston of the known piston pump has an axial bore,which extends to approximately the middle of the piston and isintersected by a transverse bore. At an orifice of the axial bore at oneface end of the piston, a valve seat made by metal cutting machining isprovided for a check valve, which in the known piston pump forms aninlet valve. The piston is a part made by metal-cutting machining in theform of drilling and turning on a lathe. The piston is complicated andexpensive to make.

ADVANTAGES OF THE INVENTION

The piston of the piston pump of the invention is a deformed part, whichis made for instance by upsetting or extrusion. In the same operation asthe production of the piston, a flow conduit is also made without metalcutting, for instance in the form of an axial hole for admitting ordischarging fluid. A valve seat of a check valve, which may form aninlet or outlet valve of the piston pump of the invention, is alsoformed onto the piston in the same operation with the production of thepiston. The valve seat can be formed on the piston on a face end of thepiston at an orifice of the flow conduit, for instance, or on an annularshoulder inside the flow conduit. Making the valve seat by deformationwithout metal cutting has the advantage of hardening the material, andthe dimensional stability and strength of the material can be increasedby a concluding swaging or reswaging of the valve seat. If the piston isguided by slide rings in the pump housing, remachining of thecircumferential surface of the piston by fine lathing, grinding, honingor the like becomes unnecessary.

The piston pump of the invention has the advantage that its piston canbe made entirely without metal-cutting machining, by deformation in asingle operation or in only a few deforming steps. This makes the pistonfast and economical to produce, and there is no waste of material.Remachining the piston surface or making bores, grooves or the like bymetal-cutting machining, which in piston production would requireadditional machining steps and machining tools, also becomesunnecessary. The valve seat hardened by deformation has the furtheradvantage of greater wear resistance and thus a longer service life.

The piston pump of the invention is intended in particular as a pump ina brake system of a vehicle and is used to control the pressure in wheelbrake cylinders. Depending on the type of brake system, theabbreviations ABS, ASR, FDR and EHB are used for such brake systems. Inthe brake system, the pump serves for instance to return brake fluidfrom a wheel brake cylinder or a plurality of wheel brake cylinders to amaster cylinder (ABS) and/or to pump brake fluid out of a supplycontainer into a wheel brake cylinder or a plurality of wheel brakecylinders (ASR or FDR or EHB). The pump is needed in a brake system withwheel slip control (ABS or ASR) and/or a brake system serving as asteering aid (FDR) and/or an electrohydraulic brake system (EHB). Withthe wheel slip control (ABS or ASR), locking of the wheels of thevehicle during a braking event involving strong pressure on the brakepedal (ABS) and/or spinning of the driven wheels of the vehicle in theevent of strong pressure on the gas pedal (ASR) can for instance beprevented. In a brake system serving as a steering aid (FDR), a brakepressure is built up in one or more wheel brake cylinders independentlyof an actuation of the brake pedal or gas pedal, for instance to preventthe vehicle from breaking out of the track intended by the driver. Thepump can also be used in an electrohydraulic brake system (EHB), inwhich the pump pumps the brake fluid into the wheel brake cylinder orwheel brake cylinders if an electric brake pedal sensor detects anactuation of the brake pedal, or in which the pump is used to fill areservoir of the brake system.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described in further detail below in terms of anexemplary embodiment shown in the drawings. shown are:

FIG. 1, an axial section through a piston pump of the invention;

FIG. 2, an end view of a tubular piston part in the direction of thearrow II in FIG. 1; and

FIG. 3, an end view of a closure plug of the piston in the direction ofthe arrow III in FIG. 1.

DESCRIPTION OF THE EXEMPLARY EMBODIMENT

The piston pump 10 of the invention, shown in FIG. 1, is inserted into ahydraulic block 12, of which only a fraction surrounding the piston pump10 is shown in the drawing. Other hydraulic components not shown, suchas magnet valves, hydraulic reservoirs and dampers of a slip-controlledvehicle brake system, are inserted into the hydraulic block 12 andhydraulically connected by the hydraulic block 12 both to one anotherand to the piston pump 10. The hydraulic block 12 forms a pump housingfor the piston pump 10 of the invention and will be called the pumphousing 12 hereinafter.

A bush 16 is press-fitted into a stepped, continuous bore 14 in the pumphousing 12. The tubular bush 16 has a bush bottom 18 that is integralwith it. A two-part piston 20, 22 is axially displaceably received inthe bush 16. The two-part piston 20, 22 protrudes for part of its lengthfrom the bush 16. On its part protruding from the bush 16, it is guidedaxially displaceably in the pump housing 12 by a slide ring 24 andsealed off in the pump housing 12 by a sealing ring 26. The slide ring24 and the sealing ring 26 are inserted into a common groove, which ismade in the stepped bore 14 in the pump housing 12.

An end of the two-part piston 20, 22 located in the bush 16 is guided inthe bush 16 by means of a second slide ring 28 mounted on the secondtwo-part piston 20, 22 and is sealed off in the bush by means of asecond sealing ring 30 mounted on the two-part piston 20, 22.

The two-part piston of the piston pump 10 of the invention is composedof: a tubular piston part 20 and a closure plug 22 firmly joined to aface end of the piston part 20. The piston part 20 has a continuousaxial bore 32, at whose orifice toward the bush bottom 18 a conicalvalve seat 34 is formed. On a face end of the piston part 20 on whichthe closure plug 22 is mounted and which is remote from the valve seat34, the piston part 20 has three grooves, distributed over thecircumference, which pass radially through an annular end face 44 of thepiston part 20 and continue axially along the inside of the tubularpiston part 20 over approximately ¼ to ⅓ the length of the piston part20. The grooves 36 extending along the inside of the piston part 20 areaccordingly open toward the axial bore 32 of the piston part 20. Thedisposition of the grooves 36 can be seen from the end view of thepiston part 20 shown in FIG. 2.

Approximately in its longitudinal middle, the piston part 20 has asealing collar 40 on its outside, as a bearing face for the slide ring28 mounted on the piston 20, 22 and, via the slide ring 28, for thesealing ring 30. The piston part 20 is a deformed part made by extrusionwithout metal cutting. Including the valve seat 34, the grooves 36, andthe radial collar 40, the piston part 20 is made exclusively bydeformation; no metal-cutting machining or remachining is done. Thevalve seat 34 can be formed on, or formed on later, by swaging orreswaging. The swaging or reswaging serves to harden the material and toimprove the dimensional stability of the valve seat 34. The grooves 36and the radial collar 40 are formed by extrusion in the production ofthe piston part 20; a separate operation is not needed to produce them.The piston part 20 has no undercuts or the like whatever, and thus thepiston part 20 can be made as a deformed part by extrusion withoutremachining.

The closure plug 22, whose end view is shown in FIG. 3, is a cylindricalpart with a short coaxial protrusion 42, integral with it, on one faceend. The closure plug 22 is press-fitted with the protrusion 42 into theaxial bore 32 of the piston part 20, and there is a press fit betweenthe protrusion 42 and the piston part 20 by means of which the pistonpart 20 and the closure plug 22 are firmly joined together.

In an annular end face 44 on which the closure plug 22 rests on thepiston part 20, at the transition from the protrusion 42 to the closureplug 22, is an encompassing groove 46, surrounding the protrusion 42,from which two radial grooves 48 extend radially outward. The radialgrooves 48, the encompassing groove 46 in the closure plug 22, the threegrooves 36 and the axial bore 32 in the piston part 22, which allcommunicate with one another, all form a flow conduit of the piston 20,22, at whose orifice toward the bush bottom 18 the valve seat 34 isembodied. The flow conduit 32, 36, 46, 48 serves the purpose of fluidadmission, in the exemplary embodiment shown here of a piston pump 10 ofthe invention. The flow conduit 32, 36, 46, 48 may, however, equallywell serve the purpose of fluid discharge, if a flow direction of aninlet valve and thus an outlet valve and hence the flow through thepiston pump 10 is reversed compared with the exemplary embodiment shown.

The fluid admission to the piston pump 10 is effected through an inletbore 50 in the pump housing 12, which discharges radially into thestepped bore 14 of the pump housing 12 into which the bush 16 ispress-fitted, and then on around the end edge 38 of the bush 16 into thebush 16 and from there through the flow conduit 32, 36, 46, 48, which isopen on the circumference of the two-part piston 20, 22, to the valveseat 34, or in other words to the face end of the piston 20, 22 towardthe bush bottom 18.

It is not necessary for both the radial grooves 48 and the encompassinggroove 46 to be made in the closure plug 22 and for the grooves 36 inthe piston part 20 to pass through the piston part radially; it sufficesfor either the radial grooves 48 and the encompassing groove 44 to bemade in the closure plug 22, or for the grooves 36 in the piston part 20to discharge axially into the encompassing groove 46. If the grooves 36in the piston part 20 pass radially through the piston part, then theradial grooves 48 and the encompassing groove 46 in the closure plug 22can be omitted. In every case, a flow through the two-part piston 20, 22from its circumference to the valve seat 34 is assured. The grooves 36in the piston part 20 are axially longer than the protrusion 42 of theclosure plug 22, so that at this location, too, a flow through thetwo-part piston 20, 22 is assured.

The closure plug 22 has no undercut at all, and so it, like the pistonpart, can be produced as a deformed part, for instance by extrusion orupsetting. A needle of a needle bearing can also be used as the closureplug 22; as a mass-produced part, it can be procured inexpensively. Thisis an attractive option, especially whenever no radial grooves 48 and noencompassing groove 46 are provided in the closure plug 22.

As its inlet valve 52, the piston pump 10 of the invention has a checkvalve, which is mounted on the face end of the two-part piston 20, 22toward the bush bottom 18. The inlet valve 52 has a valve ball 54 as itsvalve closing body, which is pressed by a helical compression spring,acting as the valve closing spring 56, against the valve seat 34 on thetwo-part piston 20, 22. The valve ball 54 and the valve closing spring56 are accommodated in a cup-shaped valve cage 58, which is made as adeep-drawn sheet-metal part and has fluid openings 60 in itscircumference and bottom. The valve closing spring 56 is braced againstthe valve cage 58. With an annular shoulder 62 on its open face end, thevalve cage 58 rests on the face end toward it of the two-part piston 20,22. The valve cage 58 is kept in contact with the two-part piston 20, 22by a piston restoring spring 64, which presses against a radial flange66 that is formed on the free edge of the valve cage 58. The radialflange 66 simultaneously acts as a bearing face for the sealing ring 30and holds the sealing ring, together with the slide ring 28, on thepiston 20, 22. The piston restoring spring 64 is considerably strongerthan the valve closing spring 56.

For driving the two-part piston 20, 22, the two-part piston pump 10 ofthe invention in a manner known per se has an eccentric element 68 whichcan be driven to rotate by an electric motor and which is disposed on aface end, remote from the inlet valve 52, of the two-part piston 20, 22in the pump housing 12 and against whose circumference the two-partpiston 20, 22 is pressed by the two-part piston restoring spring 64.

On a side remote from the eccentric element 68, a cylindrical closurepart 70 is inserted into the bore 14 in the pump housing 12. The closurepart 70 is fixed by an encompassing caulking 72 of the pump housing 12and closes the bore 14 in pressure-tight fashion. For connection to thebush 16, the closure part 70 has a cylindrical edge 74, integral with itand protruding axially away, which axially grips a collar 76 of the bush16 that protrudes past a circumference, and which is crimped inward(crimp 78).

A center hole 80 is made in the bush bottom 18, and a conical valve seat82 of an outlet valve 84 of the piston pump 10 of the invention isformed on the orifice, remote from the two-part piston 20, 22, of thishole. The outlet valve has a value ball 86 as its valve closing body,which is pressed against the valve seat 82 by a helical compressionspring acting as the valve closing spring 88. The outlet valve 84 isaccommodated in a blind bore 90 in the closure part 70. A fluiddischarge from the piston pump 10 is effected through three shallow,wide grooves 92, made in a star pattern in the bush bottom 18, whichdischarge into an annular groove 94 in the closure part 70 from whichthree radial grooves 96 extend outward in a star pattern. The annulargrooves 96 in the closure part 70 communicate with an outlet bore 100 inthe pump housing 12 via an annular conduit 98 disposed in the bore 14 ofthe pump housing 12.

The foregoing relates to a preferred exemplary embodiment of theinvention, it being understood that other variants and embodimentsthereof are possible within the spirit and scope of the invention thelatter being defined by the appended claims.

We claim:
 1. A piston pump for a vehicle brake system, comprising: apump housing (12); a check valve (52) having a valve seat (34); a piston(20, 22) that is driven to execute a reciprocating stroke motion and isaxially displaceably received in said housing, the piston (20, 22)including a tubular deformed part (20), the inside of which forms a flowconduit (32, 36), which flow conduit admits fluid at one end of thetubular deformed part, and discharges fluid at the other end; the valveseat (34) of the check valve (52) is formed onto the tubular deformedpart (20), wherein the check valve (52) prevents return flow of fluidthrough the flow conduit (32, 36); and the tubular deformed part (20)has a longitudinal groove, which groove forms the flow conduit (32, 36)at said one end of the tubular part; the piston (20, 22) also includinga closure plug (22) which is joined to the tubular deformed part (20) atsaid one end, and substantially closes the tubular deformed part (20) atsaid one end; wherein the tubular part (20) is made by a cold formingprocess without any metal cutting or removing steps, such that the coldforming process hardens the surface of the tubular part and increasesits dimensional stability and strength over what the part would have ifshaped by a metal removing process.
 2. The piston pump according toclaim 1, in which the closure plug (22) has a first slide ring (24) forguidance in the pump housing (12), and the tubular part (20) of thepiston has a second slide ring (28).
 3. The piston pump according toclaim 1, in which the groove (36) is formed by cold forming during theproduction of at least one of the tubular part (20) and the closure plug(22).
 4. The piston pump according to claim 1, in which the check valve(52) is mounted on the tubular part (20).
 5. The piston pump accordingto claim 1, in which the closure plug (22) rests against a surface of arotatable cam surface which reciprocates the closure plug and tubularpart.
 6. The piston pump according to claim 1, in which the tubulardeformed part does not have any transverse bores therethrough.
 7. Apiston pump for a vehicle brake system, comprising: a pump housing (12);a check valve (52) having a valve seat (34); a piston (20,22) that isdriven to execute a reciprocating stroke motion and is axiallydisplaceably received in said housing, the piston (20,22) including atubular deformed part (20), the inside of which forms a flow conduit(32,36),which flow conduit admits fluid at one end of the tubulardeformed part, and discharges fluid at the other end, the tubulardeformed part being formed by an extrusion process; the valve seat (34)of the check valve (52) is formed onto the tubular deformed part (20),wherein the check valve (52) prevents return flow of fluid through theflow conduit (32, 36); and the tubular deformed part (20) has alongitudinal groove, which groove forms the flow conduit (32, 36) atsaid one end of the tubular part; the piston (20, 22) also including aclosure plug (22) which is joined to the tubular deformed part (20) atsaid one end, and substantially closes the tubular deformed part (20) atsaid one end; and wherein the tubular part (20), being formed by anextrusion process without any metal removing or cutting steps, hashardened surfaces, dimensional stability and strength over what the partwould have if shaped by a metal removing process.
 8. The piston pumpaccording to claim 7, in which the tubular deformed part has notransverse bores therethrough.
 9. The piston pump according to claim 7,in which the check valve (52) is mounted on the tubular part (20). 10.The piston pump according to claim 7, in which the closure plug (22) hasa first slide ring (24) for guidance in the pump housing (12), and thetubular part (20) of the piston has a second slide ring (28).
 11. Thepiston pump according to claim 7, in which the closure plug (22) restsagainst a surface of a rotatable cam surface which reciprocates theclosure plug and tubular part.